Influence of particle composition and thermal cycling on bijel formation

Abstract

Abstract. Colloidal particles with appropriate wetting properties can become very strongly trapped at an interface between two immiscible fluids. We have harnessed this phenomenon to create a new class of soft materials with intriguing and potentially useful characteristics. The material is known as a bijel: bicontinuous interfacially-jammed emulsion gel. It is a colloid-stabilized emulsion with fluid-bicontinuous domains. The potential to create these gels was first predicted using computer simulations. Experimentally we use mixtures of water and 2,6-lutidine at the composition for which the system undergoes a critical demixing transition on warming. Colloidal silica, with appropriate surface chemistry, is dispersed while the system is in the single-fluid phase; the composite sample is then slowly warmed well beyond the critical temperature. The liquids phase separate via spinodal decomposition and the particles become swept up on the newly created interfaces. As the domains coarsen the interfacial area decreases and the particles eventually become jammed together. The resulting structures have a significant yield stress and are stable for many months. Here we begin to explore the complex wetting properties of fluorescently-tagged silica surfaces in water-lutidine mixtures, showing how they can be tuned to allow bijel creation. Additionally we demonstrate how the particle properties change with time while they are immersed in the solvents.

Inversion of particle-stabilized emulsions of partially miscible liquids by mild drying of modified silica particles

“…In a previous study [32] we began investigating the interaction between the modified silica surfaces and the water-lutidine system. We systematically varied the concentration of dye (fluorescein isothiocyanate) used to prepare the particles, finding that with increasing dye loading, the particle surfaces become more hydrophilic.…”

“…Early in the development of WL bijels we observed that if the same sample was subjected to repeated cycles of heating (phase separation) and cooling (re-mixing), the wetting preference of the particles moved gradually towards the L-phase [32].…”

“…The procedure for making bijels has been described previously [2,32]. A typical mixture was prepared as follows.…”

Dynamics and rheology of nonpolar bijels

“…In the water/oil systems, short-ranged attraction stems from the van der Waals force between particles while long-ranged repulsion is due to the weak, negative electrostatic charge of the dissociated silanol groups on the surface of hydrophilic particles (P-SNP). 20,48 When B-SNP were used to stabilize the polar bijels (e.g. bijel of nitromethane and ethylene glycol), the HMDS graft layers on B-SNP hindered the formation of monogel.…”

Particle-size effects in the formation of bicontinuous Pickering emulsions

“…This is an important consideration, as it has been shown that the presence of APTES on the silica surface is crucial for meeting the neutral-wetting requirement in the W-L system [18,19] -it has been suggested that the surface decorations act to disrupt the wetting layer of lutidine which spontaneously forms around the particles when approaching the phase separation temperature [20,21]. For the NPs, DLS returned a particle radius of 0.08 µm and TEM returned 0.063 µm with a polydispersity of 15% (Fig.…”